Rear AC Works But Front AC Not Working

[Montana Junk]

I have a 1998 Pontiac Trans Sport with 207,000 km on it and the front AC pumps out unconditioned air but the rear AC pumps out cold air. The front AC light still goes on but non conditioned air comes out of the front vents and cool air comes out the rear AC vents. The heating system on the other hand works fine for both the front and rear although the blower motor resistor needs to be replaced because fan speeds 1 and 2 don't work.

Are the front and rear AC systems connected? Do the two systems have common parts? Are the refrigerant loops seperate? Do you think it may be a damper problem at the front of the vehicle? Would the blower motor resistor affect the AC? Can anyone offer any insight?

[Hoags]

Montana Junk,
I just checked my owners manual for the 98's apparently the front and rear air systems are related. From what I could gather the rear cold air comes from the front unit. If this is the case you must have some kind of directional flow issue. As for your fan speeds it may not be the resistor I had speeds 1,2,3 & 4 quit on mine... It was the switch on the dash not the resistor. you may want to check that out first. If I rember right the switch wasn't all that expensive, but it was a dealer item.
Sorry I don't have any ideas on the front A/C problem.

[kpn]

I'm thinking the front and rear are seperate systems more than common. From under the van I see freon lines going to the rear heating and cooling unit. This tells me the compressor is probably really two compressors, one for the rear and one for the front, or it least it has special valving to divert flow to front or front/rear. My 2cents.

Keith

['97ventureowner]

Originally Posted by kpn

I'm thinking the front and rear are seperate systems more than common. From under the van I see freon lines going to the rear heating and cooling unit. This tells me the compressor is probably really two compressors, one for the rear and one for the front, or it least it has special valving to divert flow to front or front/rear. My 2cents.

Keith

If that is the case, I wonder if it is possible to "close off" the rear AC system. I had my '97 Venture recharged this past summer, and it worked fine for the rest of the day. The next day it didn't blow as cold so I took it back and the guy tested the system and said there was a probable leak. He said it is common for vehicles in our area, (heavy salt use in winter,) to have leaks in the rear lines. He said he has seen a few over the years that had this problem and that's what it turned out to be after the owners took their vehicles for further testing . I really don't need AC in the rear, so I was wondering if it could be sealed off and just use the front. I'm sure repairing this problem is expensive as everything else seems to be on these vans, and I can just imagine the cost of new AC lines.

[kpn]

Closing off the rear (if possible) still won't fix the fact that the front is not working. I'd search for a good shop in heating and ac if possible, or just take it to the dealer for a look over. It shouldn't cost much, if anything to have the dealer inspect it and give you a quote.

Keith

[Hoags]

The Systems are connected by the lines running to the rear unit. check with a pro about disconnecting the rear lines if your going to do that. you will have to find a way to seal the front half and that is a pressurized system. If not done right you will have nothing but trouble with leaks.

[sparky65]

I believe the one compressor does both though i am not shure about your year becouse in mine unless the front AC is on the compressor wont turn on no matter where the rear is set. Also if I only have the front AC on i can still hear the freon circulating through the rear. I would check to make shure it is actually closing and opening the right dampers in the front to make the are flow through the coil

[Hoags]

Sparky65, You are correct one compressor opreates the whole system and the lines running to the rear unit are the low and high pressure lines that transport the refridg. to and from the compressor. I don't thing it would be cost effective to have seperate systems. As to the original thread he has to have a directional problem with the air flow control doors. after thinking about it for awhile I do not think the system would not have a directional valve to regulate amount of refridg. that goes to the front or rear. Montana Junk is not getting the air to blow across the cooling coil in the front of the van.

[Montana Junk]

Originally Posted by Hoags

Sparky65, You are correct one compressor opreates the whole system and the lines running to the rear unit are the low and high pressure lines that transport the refridg. to and from the compressor. I don't thing it would be cost effective to have seperate systems. As to the original thread he has to have a directional problem with the air flow control doors. after thinking about it for awhile I do not think the system would not have a directional valve to regulate amount of refridg. that goes to the front or rear. Montana Junk is not getting the air to blow across the cooling coil in the front of the van.

Hoags, I think you may have pinpointed the problem although I don't know how to fix it. Could it be a vacuum line that is not opening the damper? The A/C light comes on when I hit the switch and the rear A/C puts out conditioned air. One unusual behaviour I notice is that when I used to put the air on I would notice the load on the engine momentarily... I guess as the compressor kicks in but I need to recheck this. It's winter so this work will have to wait. It may be as simple as a damper activated by a vacuum hose or perhaps the damper is motor actuated and the motor is not functioning. Does anyone have the Shop manual schematic for the AC system in a 1998 Montana or Trans Sport?

[GregA]

Originally Posted by Montana Junk

Hoags, I think you may have pinpointed the problem although I don't know how to fix it. Could it be a vacuum line that is not opening the damper? The A/C light comes on when I hit the switch and the rear A/C puts out conditioned air. One unusual behaviour I notice is that when I used to put the air on I would notice the load on the engine momentarily... I guess as the compressor kicks in but I need to recheck this. It's winter so this work will have to wait. It may be as simple as a damper activated by a vacuum hose or perhaps the damper is motor actuated and the motor is not functioning. Does anyone have the Shop manual schematic for the AC system in a 1998 Montana or Trans Sport?

I believe the 1998 models DO use vacuum to control most of the dampers, so it could be a leaking or clogged hose. Check out this page for a bit more info and some diagrams:

http://www.autozone.com/servlet/UiBr...3d801be979.jsp

Hope this helps.

Take care,

[Hoags]

Montanajunk, Sorry I havent responded to your latest post. My computer was down. Any way the 98's do use vacuum to control the damper, you may want to listen to the area around the control head. If you move the indicator to the front air position and you hear a louder rush of air you may have become disconnected at the dash. Your problem could also be at the vacuum acuator that controls the damper. I have looked at the Chilton manual and from what I can tell the control valve is going to be located on the heater/ A/C unit behind the glove box. You may have to attack it from under the dash below the glove box. I wish I could be more help.
Good luck,
Dan

If you can get a Chilton manual there looks like a pretty good diagram of the unit and controls.

[1999montana]

Originally Posted by GregA

I believe the 1998 models DO use vacuum to control most of the dampers, so it could be a leaking or clogged hose. Check out this page for a bit more info and some diagrams:

http://www.autozone.com/servlet/UiBr...3d801be979.jsp

Hope this helps.

Take care,

It could also be a coolant leak that has contaminated the plenum that houses the heater core and air con 'A' coil.

I had this happen on our '81 Olds. The coolant had leaked from the heater core into the plenum and had contaminated the damper door (the damper had open cell black foam on one side of it; - turned it to goo). The stupid foam stuck to everything!

What a mess to clean up,- in January at 20 below - outside!

[OSUCowboy27]

Make your spouse drive while you sit in the back.